Various connecting devices are known conventionally, including ball joint type linkages. A ball joint type linkage is typically used in a stabilizer and has a pair of ball joints, each of which serves as a joint device.
Such a connecting device has a pair of ball joints. Each ball joint is typically assembled from a housing, a generally rod-shaped ball stud, a bearing seat made of synthetic resin, and a dust cover. An example of processes of producing the housing is shown in FIG. 6, wherein (e) illustrates the finished housing. The ball stud, the bearing seat, and the dust cover are not shown in the attached drawings. The housing of each ball joint has a cylindrical body portion 70 and a generally cylindrical arm portion 71, which is provided as an integral body with the body portion 70 and extends from the side, i.e. the cylindrical surface, of the body portion 70. A generally spherical ball head portion provided at an end of the generally rod-shaped ball stud is contained in the body portion 70 of the housing, with the bearing seat disposed between the ball head portion and the body portion 70.
The cylindrical body portion 70 of the housing is formed in a cylindrical shape having an opening 72 and an insertion hole 73 for containing the ball head portion of the ball stud. The stud portion, which integrally extends from the ball head portion of the ball stud, is adapted to be inserted through the opening 72. The housing includes a blocking plate (not shown) to close off the insertion hole 73 so that the inside of the housing serves as an inner chamber for containing the ball head portion. A cover attaching portion having a cylindrical shape is formed along the rim of the opening 72 of the body portion 70. The aforementioned dust cover is fitted and fixed to the cover attaching portion. A stopper portion 75 is formed along the rim of the insertion hole 73 of the body portion 70. The ball joint described above is assembled by placing the ball head portion and the bearing seat in the inner chamber, subsequently crimping the stopper portion 75 inward, and attaching the blocking plate to the housing.
The connecting device also includes a rod-shaped connecting member provided with fitting portions which are generally in the shape of a solid cylinder and respectively located at the two axial ends of the connector portion. Two ball joints respectively assembled as above are connected to the connector portion by snugly inserting each fitting portion of the connector portion into the end of the arm portion 71 of the housing of each ball joint so that there is a given distance between the respective centers of the two ball head portions and, in this state, integrally welding the fitting portions to the respective arm portions 71. Thus, the connecting device is formed.
The process of producing a ball joint housing described above consists of steps described hereunder. First, a rod-shaped working material 80 shown in FIG. 6(a) is undergoes upsetting, in other words, pressure is applied in the axial direction to an axial end of the working material 80 while the other axial end of the working material 80 is secured so that the diameter of the said other axial end and its vicinity remains unchanged. As a result of the upsetting process described above, the earlier mentioned end of the working material 80 is pushed and deformed. Thus, a first-stage intermediate formed body 83 shown in FIG. 6(b) is formed by forging. The first-stage intermediate formed body 83 consists of a stem portion 81 and a head portion 82, which has been formed at an end of the stem portion 81 by the aforementioned deformation and has a diameter greater than the stem portion 81. Then, a generally cylindrical first-stage preliminary body portion 84 which is open at the bottom and closed off at the top is formed by applying pressure to the head portion 82 of the first-stage intermediate formed body 83 in a direction to intersect the axial direction. Thus, a second-stage intermediate formed body 85 shown in FIG. 6(c) is formed by forging. Thereafter, a third-stage intermediate formed body 88 shown in FIG. 6(d) is forged by applying pressure in the axial direction to the first-stage preliminary body portion 84 of the second-stage intermediate formed body 85 to form a cylindrical second-stage preliminary body portion 87 having a preliminary hole 86 at the top thereof. Then, the aforementioned body portion 70 is formed by applying pressure in the axial direction to the second-stage preliminary body portion 87 of the third-stage intermediate formed body 88. The stem portion 81 is formed into the arm portion 71 by boring an axial hole 89 in the stem portion 81 in such a manner that the axial hole 89 extends coaxially with the stem portion 81. Thus, a socket body 91 shown in FIG. 6(e) is formed.
In the course of producing the socket body 91 of the connecting device according to the conventional production process described above and illustrated in FIG. 6, the arm portion 71 of the ball joint housing is formed by boring an axial hole 89 in the stem portion 81, which is in the shape of a solid cylinder. For this reason, the conventional production process hinders improvements in manufacturability.
In order to solve the above problem, an object of the present invention is to provide a joint device which enables improvements in manufacturability. Another object of the present invention is to provide a method of producing a housing of such a joint device.